Transducer



May 12, 1953 w. T. HARRIS 2,633,577

TRANSDUCER Filed Nov. 15, 1949 2 Sheets-Sheet 1 FIG. I. /a l6 4 a 3 III. INVENTOR A71 1/ W/LBU HARE/5 ATTORNEYS May 12, 1953 w. T. HARRIS 2,633,577

TRANSDUCER Filed Nov. 15, 1949 2 Sheets-Sheet 2 lNVENTOR W/LBUR 7. HARRIS A ORNEYS Patented May 12, 1953 NHTED ST Tss arr FFHCE TRANSDUCER Application November 15, 1949, Serial No. 127,437

19 Claims.

My invention relates to transducer means, as for translating mechanical wave energy, sonic or supersonic, into electrical energy, or vice versa.

It is an object of the invention to provide an improved means of the character indicated.

It is another object to provide an improved transducer for converting underwater sound into electrical energy and vice versa.

It is also an object to provide a more efficient transducer construction of the character indicated.

It is a further object to provide an improved unitary transducer construction having particular adaptability for the construction of multipleunit arrays, as when a more sharply defined directional response is desired.

It is a general object to provide a relatively inexpensive transducer-element construction having high efiicienc and capable of substantial abuse without impairment of response.

Other objects and various further feature-s of novelty and invention will be pointed out or will become apparent to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred forms of the invention:

Fig. 1 is a more-or-less perspective View in partial section of a transducer unit incorporating features of the invention;

Fig. 2 is a longitudinal sectional view of a transducer such as that of Fig. 1 during the process of assembly;

Fig. 3 is a perspective view, partly broken-away and partly in section, of principal elements of a transducer of modified construction, the elements being shown in partly separated relation, as during a step in the assembly of the transducer;

Fig. i is another partly broken-away perspective view, showing a further modified construction with certain elements partly removed as during a step of assembly;

Fig. 5 is a fragmentary view in partial section of an array of transducer units of the aboveidentified embodiments, the transducer units being shown in side elevation; and

Fig. 6 is an electric circuit diagram representing an electrical analogy of electro-mechanical relationships within a transducer of the invention.

Briefly stated, my invention contemplates a transducer construction in which a generally axially or longitudinally travelling pressure wave may be caused, through a suitable transforming medium, to produce radial deformations or stresses in a cylindrical member, and electrical means are provided to respond to such deformations or stresses. The efficiency of transformation from longitudinal excitation to radial excitation may be enhanced by employment of suitable counterweight or backing means longitudinally spaced from the end of the cylinder from which the pressure wave originated. In transducers for underwater-sound applications, the cylinder may be freel flooded with water or other fluid, but in the present arrangements I employ a relatively non-compressible effectively-fluid medium within the cylinder and in contact with the counterweight or backing member. The counterweight and, if desired, a diaphragm may effectively close off the longitudinal ends of the cylindrical memher; and the natural resonance characterizing the coupling between the counterweight (and diaphragm, if used) and the medium Within the cylindrical member is preferably at a different frequency than that of the natural radial-flex resonance of the cylindrical member, so that a broad-band response may be achieved.

In the forms to be described, the electricallyresponsive means is supported upon an openended generally cylindrical member, which memher is in effective pressure-responsive relation with the efiectively fluid material. In one form, the cylinder is of magnetostrictive material, and the electrical means is a toroidal winding about the cylinder as a core. In another form, the cylinder is of electrostrictive material, and the electrical means includes radially opposed spaced plates or electrodes on the inner and outer surfaces of the electrostrictive material. In a third form, a circumferential length of a material electrically sensitive to strain is applied to the outer surface of the cylinder.

Referring to Fig. 1 of the drawings, my invention is shown in application to a transducer having particular utility in underwater-sound applications. The transducer may comprise a generally cylindrical member HJ having open ends and to be subjected to radial stresses or deformations or striations. One end of the cylinder 10 may be effectively open to the sound-transmitting medium, but in the form shown I employ relatively thin, low-mass diaphragm means H which may include a piston portion l2 mechanically isolated from the cylinder [0 and covering substantially the entire internal cross-section of the cylinder I0. At an axially spaced location away from the piston l2 the cylinder l0 may be effectively closed off by a counterweight or backing member [3 which is preferably of high mass and stiffness; in the arrangement shown, the counterweight member 13 effectively closes off the opposite end of cylinder 10.

In order to derive an electric output reflecting transient radial stressing of the cylinder member It, I have in the form shown in Fig. 1, employed magnetostrictive material in the construction of the cylinder l0, and a toroidal winding M of insulated wire terminating in leads l5 may be applied about the cylinder [8 as a core. The winds la s r e to ma cally mlariaine he core in. The magnetostrictive material of the core l0 may be of laminar construction, as will be explained.

The interior of the cylinder i9 is preferably filled with a relatively non-compressible sound: transmitting medium. If desired, this interior may be flooded with oil or with Water so as to obtain an intimate pressure-transmitting relation between the medium I6 and the diaphragm ll, counterweight l3, and cylinder lily. the form shown, however, and in order to achieve a unit-handling relation for the entire transducer unit, I have employed so-called rho-c rubher as the filler medium H5. Such rubber will be understood to have the sound-transmitting characteristics of water, which will be assumed to be the medium in which sound is to be detected or projected via the transducer.

I order to render the transducer responsive substantially only to diaphragm displacements, the outer circumference of the wound core ill,

may be enveloped by sound-absorbing or ate a tenuating means, and in the form shown I have employed an air-filled rubber or rubber-like blanket l1 substantially enveloping th cylinder. In the event that rubber or rubber-like material is employed as the filling means l6, I- prefer that such means [6 shall fill the cylinder homogeneously (as to sound-transmitting characteristics). with an integral bond to. the parts H- l3-.lll, so as to permit good pressure-transmitting relationships between these members via the medium I6.

In the preferred form shown in Fig. l, the magnetized magnetostrictive cylinder is preferably composed of thin concentric cylinders of magnetostrictive material. I hese separate cylindrical laminations may be bonded together into a mechanically unified mass; nickel, and alloys of nickel and iron and cobalt possesses the desired properties. Alternatively, the laminated cylinder can be produced bywinding a suitably coated magnetostrictive sheet on a mandrel until the desired wall thickness is produced, and this step may be followed by a baking or firingprocess in order to producesolid bonding. Lamination is desirable for high efiiciency because eddy currents within the magnetostriotive material are thereby reduced,

In the construction of transducer units such as shown in Fig. 1, one may separately produce h i a fc H? b o 91? th ethod o ed above, n he drq da ndin It ma then be applied. In toroidally winding'the core I P r m o e ul l rred Pierce "if of i ul n ma e ial. fit in v r. the end of if? min n as embl i orde to pr vent sulat ee failures h Willdipg Wil a 116, har st tomes of th rns As a se ar te as emb n ref in t F the P on 9. dia hra m m ans H m rst be a .ser .e v to t e co nter e ht mean i as b elnploynleilt 0i ied means 151. n the fo h the i d i hreaded n t a shoulder 2| at the bottom of a counterbore the counterweight l3, and a longitudinally projecting extension 22 of reducedsection is centrally threaded into the diaphragm means H.

: rubber filler, as by 4 Both threaded engagements are preferably of the same pitch, so that if later disassembly is desired, the rod 26 (including its extension 22) may be removed without upsetting the spaced relation of the diaphragm means H and of the counterweight means it.

In one form of the invention, it may be use- 1. t have th ra m and coun e mechanically linked to each other, as by means of the tie-rod 22; and in such event the fit of ti e-rod 22 to the members H--l3 may be made tight and permanent, as by welding, swaging, er ether means (not specifically shown). If the tie-rod 22 is to remain a permanent part of the finished transducer, then the tie-rod 22 is preferably coated with a cement so that the rubber for the medium l5 may be intimately bonded thereto; if, on the other hand, the rod 22 is'to be removed so as to produce the transducer of Fig. 1, then the rod 22 is preferably coated with parting means rather than with a cement. Such parting means may include an application of stearic acid, followed by a wrapping of cello, phane. over the rod.

Having suitably coated or otherwise treated the surface to be bonded to the rubber-like medium [6, the volume to be'rubberefilled may be built up, as by spirally winding the tie-rod 22 with calendered sheets of tacky raw-rubber come pound. The raw rubber may be built up to an excessive thickness and tightly bandaged with cloth tape. The assembly may then be placed in an autoclave and subjected to high gas pressure as the temperature. is raised, in order to consolidate the rubber (eliminate porosity and bubbles) and to bring about vulcanization. When vulcanization is complete, the autoclave is gradually cooled and the gas pressure lowered. When cool, the assembly may be mounted in a lathe, utilizing the rod 29 for centering purposes, and the. cylindrical rubbersurface maybe ground to such size that the wound magnetostrictivev element lill i may be put in place as illustrated in Fig. 2. A rubber sleeve '23 may then be applied over the winding [4, and such sleeve may have provision for bringing out the leads IS. A polymerizable liquid, such as a styrene compound, may then be run in and degassed, and polymerization may be allowed to take place in order to establish an intimate in: tegral bond between the elastic filler i6 and the sleeve 23. The rubber cover its may then be removed and the air-filled rubber-like blanket i! applied and cemented in place.

Glearly, alternative methods of applying the injection molding may be evolved.

The interior of the transducer must be solidly filled, so that forces applied to the diaphragm (or to the open end, if no diaphragm isfei'nrployed) can produce radial application of pressure on the cylinder essentially without loss. Therefore, if the rod 22 is to be removed, the hole left by the rod should be filled solidly with a rubberor rubber-like material. Theoretical analysis has shown, as noted below, that, by of the rod 22 in a' transducer of the character indicated, efficient response is essentially limited to the higher frequencies and that for maximum efficiencyover a broad frequency range the rod 22 shouldbe removed. After removal the rod 22-, the hole left by the rod 22 m y be fiuii with apolymerizable synsthetic rubbery potting compound," and a plug 24' may be screwed into the oounterbore of the counterweight l3.

n a y p s i g" a r e electr c current through the winding M, the magnetostrictive element It] may be magnetized; then, with suitable mounting and amplifying equipment, the complete transducer is ready for use.

With certain simplifying assumptions (e. g. that the length of the sensitive hollow cylinder be a fraction of the wave length), mechanical characteristics for a transducer of the character indicated may be computed, and its performance predicted. For example, consider a transducer of the following dimensions: a diaphragm diameter of in.; a piston diameter of 8 in. approximately; an inside diameter of 8 in. for the magnetostrictive cylinder; a cylinder-wall thickness of 0.2 in.; Youngs modulus for the cylinder material, 16 10 dynes/cmfl; length of cylinder, 6 in.; a counterweight piston of 8 in. diameter by 3 in. thick steel; a diaphragm-piston assembly of mass 1000 g.; stiffness presented to the diaphragm due to radial expansion of the magnetostrictive cylinder is 3.33 10 dynes/cm.; compressibility of rubber filling 80 10 of volume per dyne/cmF.

In making a theoretical analysis of my transducer, an electrical analogy may be helpful, and Fig. 6 is a simplified representation. In Fig. 6, V1 represents the alternating pressure on the diaphragm, 1211, the diaphragm and piston mass. ii the diaphragram velocity, Cr the reciprocal of the stiffness presented to the diaphragm by the From these equations a relationship between the frequency and the velocity (i2) of the sensitive element may be derived, assuming a constant amplitude of the alternating sound pressure (V1) on the diaphragm. Making use of this relationship, an approximate frequency response may be deduced, as follows:

I, cycles/sec. i2, cm./sec. l0"

100 7'2. 9 159 730 168 w 200 j8. 8 812 j0. 96

Thus, the open-circuit voltage response may be substantially flat or uniform in the region below where f1 and f2 are respectively the frequencies where the low frequency and high frequency resonances occur.

If an axial steel rod of 0.5 in. diameter rigidly connects the diaphragm and counterweight (e. g. rod 22), the diaphragm stiffness is increased more than 50-fold, and. the efiiciency of the transducer is impaired at frequencies below 800 cycles per sec.

The described transducer unit may find application as a single unit as in seismic applications, but in underwater-sound applications the unit is particularly useful in multiple-unit arrays, so as to achieve directionally responsive characteristics. For sake of illustration, I have shown in Fig. 5 two adjacent units of such an array. In the form shown, the entire array is included within a suitable tank or vessel having a back wall 25 and a front wall 26, either of which walls may form part of a ships outer hull structure. The front wall 26 may be pierced with a plurality of Windows 2'! through which the open ends or diaphragms H of the various transducer units may be permitted effective contact with the outside fluid medium. In the form shown, I have employed rubber-like Window means 28 bonded to the diaphragms II and mounted, as by clamping rings 29 and mounting bolts 30, to the rims of the windows 21. Back support for the transducer units may be provided by cradling the counterweight means l3 within annular flanges 3| which may be secured by welds 32 to the back plate 25. I prefer that the relation between the counterweight means l3 and the back plate 25 shall involve as poor a sound-transmitting character as possible, and in the form shown I have employed a cup 33 of sound-attenuating means such as air-filled rubher to provide the necessary spacing support for the counterweight 13. The assembled array may be completed either by free-flooding the interior of the tank with the fluid (e. g. water) into which the array is to be immersed or by filling the tank with castor-oil or the like.

I have described my invention in considerable detail in connection with a magnetostrictive embodiment, but it will be understood that the principles of the invention are of equal application for constructions employing other means of electro-mechanical energy transformation. In Fig. 3, for example, I have shown a transducer construction in which the diaphragm ll, piston I2, counterweight l3, and elastic medium l6 may be of the same general form as that previously described, but in which electrostrictive phenonema are employed for electro-mechanical energy transformation. Thus, the core of the electrical part of the transducer may comprise a cylindrical member 35 of an electrostrictive material, such as barium titanate. The cylindrical memand 10. In a transducer of the character indicated, a hollow open-ended generally cylindrical member, a counterweight member of relatively high mass and stillness effectively closing one end of said cylinder and mechanically isolated therefrom, effectively fluid means having relatively good sound-transmitting characteristics Within said cylindrical member and in intimate pressuretransmitting relation with said counterweight member and with the inner wall of said cylindrical member, the resonant frequency characterizing longitudinal coupling between said counterweight member and said fluid means being substantially different from the natural radialresonance frequency of saidl cylindrical member, means electrically responsive to radial strictive displacement of said cylindrical member, and sound-attenuating means surrounding said cylindrical member.

11. A transducer according to claim 10, in which sound-attenuating means is applied in back; of said counterweight member, whereby except for the end opposite said counterweight member said transducer may be effectively enveloped by soundattenuating means so that the difierence in compliance between mediums on opposite sides of said counterweight member and of said cylindrical member may enhance the broad-band response of said transducer.

12. A transducer according to claim 2, in which said cylindrical member is of generally cylindrically laminated magnetostrictive material.

13. A transducer according to claim 12, in which said laminations are concentric cylinders.

14. A transducer according to claim 12, in which said laminations comprise a helical winding of sheet material to effectively form a plurality of cylindrical laminations.

15. In a transducer of the character indicated, a relatively thin-walled generally cylindrical hollow member, electric means responsive to radially stressed deflections of said member, a diaphragm longitudinally freely suspended and effectively closing one end of said member and mechanically isolated therefrom, and a longitudinally freely suspended counterweight member mechanically isolated from the other end of said cylinder and eflectively closing said other end, said diaphragm member and said counterweight member being mechanically interconnected.

16. In a transducer of the character indicated, a relatively thin-walled hollow open-ended cylindrical member of electrostrictive material, an electrode on the outer surface of said cylindrical member, a second electrode generally radially opposed to said first electrode and on the inner surface of said cylindrical member, counterweight means substantially closing one end of said cylindrical member, and sound-transmitting eifectively fluid means associated with said counterweight means and with the inner Wall of said cylindrical member.

17. A transducer according to claim 2, in which said last-mentioned means includes a circumferentially extending length of a conducting material whose conductivity is sensitive to strain.

18. In a transducer of the character indicated, an open ended generally cylindrical thin-walled member, counterweight means effectively closing one end of said cylindrical member and mechanically isolated therefrom, diaphragm means effectively closing the other end of said cylindrical member and mechanically isolated therefrom, electric means responsive to radial strictive deformations of said cylindrical member, and a relatively incompressible rubber-like medium in sound-transmitting relation with said diaphragm and with said counterweight means and with the inner wall of said cylindrical member, the natural longitudinal and radial resonance frequencies of said parts in conjunction with said medium being substantially different, whereby broad-band response may be achieved.

19. In a transducer of the character indicated, two mechanical oscillators of substantially different resonant frequencies, elastic coupling means between said oscillators, whereby each oscillator may exhibit both resonant frequencies, and electrical means responsive to oscillations of one of said oscillators, said one oscillator comprising an elongated cylindrical member filled with and in intimate relation with sound-transmitting material, and the other of said oscillators comprising a counterweight longitudinally freely suspended at one end of said cylindrical member and in intimate relation with said soundtransmitting material.

WILBUR THOMAS HARRIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,005,741 Hayes June 25, 1935 2,076,330 Wood et al. Apr. 6, 1937 2,116,522 Kunze May 10, 1938 2,438,925 Krantz Apr. 6, 1948 2,480,535 Alois et al. Aug. 30, 1949 2,497,901 Mott Feb. 21, 1950 

